DONAX. 403 



it an octagonal appearance ; these lines terminate at the orifice 

 in eight small fimbriated prongs, which fold over and enclose 

 the tube whenever anything passes into it ; the excurrent tube 

 has only six of these lines and as many terminal prongs ; 

 when the tubes are withdrawn, they are protected by a small 

 pouch formed out of the mantle ; siphonal orifices and cirri of 

 a very pale orange colour : gills large, suboval, light brown ; 

 upper pair much smaller and shorter than the lower : palps 

 rather long, triangular, pale yellow, smooth externally and 

 distinctly striated internally : foot very large, much compressed, 

 bevelled to a sharp edge and lanceolate point when fully ex- 

 tended ; but when at rest or half exserted, it is puckered and 

 transversely ridged. 



Shell triangularly oblong, not very inequilateral, somewhat 

 compressed but more convex towards the beaks and sloping 

 from that part to the margins, rather thick, opaque, glossy and 

 polished: sculpture, numerous fine longitudinal stria?, which 

 radiate from the beak but do not extend to the anterior or 

 larger side, and only cover about two-thirds of the surface ; 

 they are more crowded on the posterior slope ; the posterior 

 side is also marked with a few concentric or transverse stria?, 

 which are scratch-like and veiy irregularly disposed, never 

 reaching to the ventral area ; these last stria? are usually 

 llexuous, and observable on one or more parts of the posterior 

 area but never on all parts of it ; they are not found in the 

 earlier stages of growth, and occasionally (but rarely) they are 

 altogether wanting ; where the two sets of stria? intersect each 

 other a partial decussation is of course the result : colour 

 yellow, brown, or purple of different shades, often variegated 

 (especially in the young and half- grown specimens) with three 

 rays of white, one proceeding from the beak, another crossing 

 the ventral range, and the third running along the posterior 

 ridge ; the lines of growth are generally marked by broad con- 

 centric bands of a deeper hue ; sometimes the colour is uni- 

 form milk-white : epidermis thin and smooth, like varnish, 

 delicately and microscopically striated in a transverse direc- 

 tion : margins gently curved in front, with a slight indentation 

 or sinuosity near the posterior side, which is gibbous, strongly 

 angulated, obliquely but not abruptly truncate, and ends in a 

 blunt and somewhat rounded point ; the ridge which encloses 

 a great part of this side is prominent and extends from the 

 beak in each valve, enclosing a kind of enormous lunule with 

 projecting lips; anterior margin semioval and wedge-shaped; 



